This invention relates to the wall structure for the test section of a wind tunnel. The wind tunnels which have a test section with perforated walls enclosed completely in a plenum chamber, the plenum chamber can be evacuated to allow part of the tunnel main flow to be removed through the perforated walls of the test section. This provides a means for the attenuation of disturbance waves when the wind tunnel is operating above sonic speeds.
High speed flow parallel to walls having cavities or perforations will cause edgetones to emanate from the wall. Each of the holes generates a tone, with the entire wall producing tones in phase, with strong resonance amplication between opposite walls intensifying the noise.